Method for the production of sheets of stratum corneum

ABSTRACT

An intact sheet of stratum corneum is obtained by placing a piece of adhesive tape bearing stratum corneum which has been removed from the skin of a donor upon a fine screen with the stratum corneum in contact with the screen. The tape/stratum corneum composite is then continuously washed with a solvent which exerts a softening effect upon the tape adhesive. When the adhesive is sufficiently soft, the tape is removed from the stratum corneum.

United States Patent 1191 Turek Oct. 16, 1973 METHOD FOR THE PRODUCTION OF SHEETS OF STRATUM CORNEUM [75] Inventor: Bohuslav Turek, Paris, France [73] Assignee: Richardson-Merrell Limited,

London, England [22] Filed: Apr. 17, 1972 [211 App]. No.: 244,560

[30] Foreign Application Priority Data Apr. 19, 1971 Great Britain 10,003/71 [52] US. Cl. 128/2 R, l95/l.8, 23/253 TP [51] Int. Cl A6lb 10/00 [58] Field of Search 128/2 R, 2 W, 2 B;

l95/l.7, 1.8; 23/253 TP [56] References Cited FOREIGN PATENTS OR APPLICATIONS l/1966 Great Britain 128/2 W 1,212,404 l0/l959 France ..128/2W OTHER PUBLICATIONS Studies on Oxyuriasis-American Journal of Tropical Medicine-Vol. 17 Pages 445-453 by Maurice C. Hall-Nov. l8, l936-Dated 1937.

Primary Examiner-Aldrich F. Medbery AttorneyE'. F. Wenderoth et al.

[57] ABSTRACT An intact sheet of stratum corneum is obtained by placing a piece of adhesive tape bearing stratum corneum which has been removed from the skin of a donor upon a fine screen with the stratum corneum in contact with the screen. The tape/stratum corneum composite is then continuously washed with a solvent which exerts a softening effect upon the tape adhesive. When the adhesive is sufficiently soft, the tape is removed from the stratum corneum.

3 Claims, 4 Drawing Figures PATENTEDUBT 16 1915 3.765404 sum 10F 2 PMENTED BET 16 I973 SHEET 2 [IF 2 llln' METHOD FOR THE PRODUCTION OF SHEETS OF STRATUM CORNEUM The present invention relates to a method of and apparatus for obtaining fine, substantially unfissured, coher'ent sheets of stratum corneum. (horny layer) from human skin.

Some coherent sheets are of great interest for the preliminary in vitro inspection and testing of consumer products intended to be applied to the human-skin or which may accidentally come into contact with the human skin. Although the stratum corneum is not formed of living tissue, it nevertheless exercises a pronounced protective effect on the underlying skin tissue. In consequence any product which has the effect of removing or damaging the stratum corneum is likely to be most unsuitable for contact with the skin, since the application of such product will remove or diminish the protection normally provided by the stratum corneum to the underlying living tissue. It can therefore readily be understood that a thinintact layer of stratum corneum, particularly of a thickness of about microns, is of great interest for the preliminary, in vitro, examination of new products, such as sun tan lotions and cosmetics and enzyme-containing products. The advantage of the in vitro examination of new products by using coherent sheets of stratum corneum lies primarily in the much more exact but, at the same time, more versatile assessment of several parameters which are important in determining either the products efficacy for instance, their substantivity to the horny layer, their moisturising effect, their ultra violet screening effect, their influence on the horny layer sloughing-off process or their possible deleterious effects. If the products studied are found, by in vitro tests, to have a beneficial effect on an intact sheet of stratum corneum, then their use would be likely to produce a similar effect in vivo. Similarly, the possible deleterious effects on the products can be studied invitro on a sheet of stratum corneum prior to in vivo tests. If the products are not found in vitro to have a harmful effect on the intact sheet of stratum corneum, then it is possible to proceed with greater confidence to the in vivo examination of the effects of products of a similar nature. Conversely, if a product is found, by in vitro examination, to have an unwanted effect on the intact sheet of stratum corneum, then this product can be eliminated prior to the much more difficult and expensive in vivo sheets. It will in consequence be apparent that any method which enables a coherent layer of stratum corneum to be obtained is of considerable economic importance. It is particularly desirable to be able to provide intact layers of a thickness of about 10 mircons, because of the possibility of studying such layers very easily under the microscope. There is no need for providing refined methods for splitting the very fine sheets of stratum corneum provided by the method of the present invention.

It is already known that the outer layers of stratum corneum may be removed by the application of a plastic tape, coated with pressure sensitive adhesive, to a selected area of the skin. This technique has been employed where it has been desired to expose the lower layers of the skin and thus provide a somewhat hypersensitive area of living tissue on which to test the effects in vivo of the topical application of various products or to study the isolated horny cell groups of microscopic 2 size. The results of the process of the present invention are totally different.

It will be found on microscopic examination of the pressure-sensitive tape employed in the known method that the layer of stratum corneum is in a fissured condition and thus it would be of little value for the purpose above stated, even were there a satisfactory existing method of removing the layer of stratum corneum from pressure sensitive tape. it is to be emphasised that the known method is perfectly satisfactory for its purpose, that purpose being in no way affected by the fact that small fragments of stratum corneum may have been left on the skin area.

The present invention is based on the realisation that a complete sheet of stratum corneum may be removed from the skin by the use of pressure sensitive tape, provided that special care is taken, and that such sheet hesion of the pressure sensitive tape to the skin has been found to be the application of gentle heat and pressure over a prolonged period. For example, complete adhesion has been obtained by the use of a metal block, which is heated to a temperature of between C. and C. and is of a weight sufficient to exert a pressure of about gms/cm. The tape is first ironed onto the selected area of the skin to ensure that there are no wrinkles in either the tape or the skin; the necessary pressure is exerted by a heated metal block, which is held stationary for about five minutes on the uppermost side of the tape. After removal of the block, the tape must stay in place for a period of at least two hours. At the same time, care must be taken to reduce as much'as possible the movements of the area covered with tape (excessive movement would produce fissures), by keeping the donor as still as possible. After this period the tape is peeled off and a sheet of stratum corneum is found to be attached to it.

The above method has been found satisfactory for the removal of a satisfactorily intact sheet of stratum corneum using currently available pressure-sensitive adhesive cellulose tapes. it is to be emphasised that any other procedure for the removal of an unfissured sheet of stratum corneum on an adhesive tape would be satisfactory for the present invention provided that the adhesive on the tape was not irreversibly set in carrying out the process, since the soft pressure-sensitive adhesive layer on the tape is softened by solvents in the subsequent processing of the tape to separate the sheet of stratum corneum.

The invention is primarily concerned with the procedure for the removal of the sheet of stratum corneum,

thus obtained, from the adhesive carrier tape without Thus according to the presentinvention a method of obtaining a substantially intact sheet of stratum corneum comprises, in a first stage, separating an intact sheet of stratum corneum from a human donor by means of adhesion to a carrier tape and, in a second stage, separating the. sheet of stratum corneum from the carrier tape by a peeling method which comprises: placing the carrier tape/stratum corneum sheet composite unit on a fine screen, arranging the composite on the screen so that there is an uncovered area of the screen entirely surrounding the composite unit, the stratum corneum being in contact with the screen; supplying solvent liquid in a continuous stream to the top surface of the composite to maintain a covering of liquid over the composite to replace the liquid flowing through the area of the screen surrounding the composite,'while lifting one edge of the composite sheet to just raise the edge of the underlying stratum corneum from the screen to initiate the separation of the carrier tape from the stratum corneum and thereafter carefully peeling the carrier tape from the sheet of stratum corneum. Once the separation of the carrier tape from the stratum corneum is initiated, the downflow of liquid pulls the loose, unsupported edge of the stratum corneum onto the screen and the liquid exerts a wedge action between the stratum corneum and the carrier tape to assist and advance the peeling operation.

In carrying out this operation it is preferable to apply suction below the screen so as to increase the pressure differential which acts to hold the composite down onto the screen. It is generally preferable that the liquid should exert some softening or solvent action on the adhesive, but of course must not have any solvent or similar action on the sheet of stratum corneum.

In order to carry out the operation in the most effective manner it is preferred that the flow of liquid around the edge of the composite should be as free of turbulence as possible and for this reason it is preferred to avoid liquid flow across the top of the composite. This is best achieved by feeding liquid over a weir surrounding the screen so as to maintain an annular stream downwards'around the periphery of the composite unit, whilst there is virtually stationary pool of liquid over the top of the composite.

An apparatus for putting the present invention into effect and a method of using such apparatus is illustrated, partially diagrammatically, in the accompanying drawings, wherein:

FIG. 1 is a section of an apparatus made in accordance with the invention, and

FIGS. 2, 3 and 4 illustrate the sequence of steps employed in separating the layer of stratum corneum from the carrier tape. 1

The apparatus comprises a body 1, which is circular in shape and has a liquid inlet 2 and an outlet 3. The

inlet 2 supplies liquid to a shallow trough 6, having a weir edge 5, over which the liquid spills. it will readily be understood that in use the apparatus must be properly levelled to ensure the proper flow of liquid at a substantially even rate around the periphery of the trough.

In the conical lower part 6 of the body there is preferably placed a magnetic member 7, preferably in the form of a cross or ring. This ring is free from the body 1. At the upper margin of the lower part 6 is formed a series of radially directed, spaced ribs 8, which form a platform for a screen b. Similarly a second series of ribs 8a are arranged to support a larger screen 9a. in carrying out the separation operation only one of the screens 9, 9a are employed, the screen being selected so as to match and slightly overlap the surface form of the composite unit. The screens are circular in shape, whereas the composite units are, in general, rectangular (because the tape is cut into rectangular pieces). The necessaray matching of circular screen and rectangular composite unit is achieved by applying a thin layer of impervious material to that part of the screen surrounding the composite, but leaving a narrow gap for liquid flow.

In operation, magnetic member 7 is put in position and the selected screen, which is in the form of a disc, made of stainless steel (or other materials), with an appropriate pattern of apertures, is placed on the appropriate rings or-ribs 8 or 8a. The flow of liquid is then commenced. At this moment the position is as diagrammatically illustrated in FIG. 2.

When the liquid has built up to an appropriate level over the composite and the softening action of the liquid (if any) has taken effect on the adhesive of the carrier tape a at and around the edge of the stratum corneum sheet b, a valve 10 is opened and liquid is steadily withdrawn by pump and re-circulated to the liquid inlet 2. The projecting edge portion a of the carrier tape is then grasped by means of a forceps and raised very gently to the position illustrated in FIG. 3, in which the edge of the stratum corneum is lifted just clear of the screen 9. in this position, the liquid flow through the area of screen 9 adjacent to the edge of stratum corneum sheet b exerts a downward and-outward pull, indicated by arrow 11, on the upturned marginal portion of sheet b which initiates the separation of tape a and sheet b. The downward pull exerted by the liquid pulls the sheet b down onto the screen 9 as the flexible carrier tape a is slowly peeled back by means of the forceps by which it is grasped. The sheet b is held down onto the screen by reason of the pressure differential across the screen 9. Tape a can be progressively peeled from stratum corneum sheet b without damage, providing sufficient care is exercised and the peeling force applied to tape a is insufficient to separate sheet 12 from the screen 9.

' When'the peeling of tape a is completed, the screen 9 supporting the stratum corneum sheet b is lifted out of the body 1 by means of a magnet, which lifts the magnetic member 7. After removal from the body, the magnet may be separated by removing the magnetic member from the reverse side of the screen 9. The stratum corneum sheet b is then dried on the screen and removed from the screen when dry.

The apparatus and the manner in which it is used are clearly capable of alterations in a number of ways. Thus it is possible to maintain reduced pressure below the screen 9 by a separate application of vacuum.

Where it is desired to increase the pressure differential across the screen 9, a separate flexible teflon screen, having finer drainage apertures, may be placed over the screen 9.

It, will readily be understood that the described method and apparatus may be employed for separation of other fine films or sheets from backings to which they are adhered by means of a soft adhesive.

Suitable solvent liquids for use in the process of the present invention are hexane, toluene or a mixture of both. These are suitable for softening the pressure sensitive adhesive employed on normal, commercially available cellulose tapes coated with pressure sensitive adhesive.

I claim:

I. A method of producing a substantially intact sheet of stratum corneum comprising the steps of applying a tape, bearing a pressure-sensitive, solvent-softenable adhesive, to a selected area of the skin of a human donor under conditions of heat and pressure, maintain ing said tape on the skin of the donor for a prolonged period and removing said tape from said skin bearing an intact, unfissured layer of stratum corneum supported thereon, placing the carrier tape/stratum corneum composite unit on a fine screen in such manner that an uncovered area of the screen entirely surrounds the composite and the stratum corneum is in contact with said screen, supplying a solvent fluid, which exerts a softening action on the pressure-sensitive adhesive, in a continuous stream to the upper surface of said screen to maintain a covering of fluid over the composite unit and replace fluid passing through said screen, while lifting one edge of the composite to just raise the edge of the underlying stratum corneum from the screen to initiate separation of the carrier tape from the stratum corneum sheet and thereafter carefully peeling the carrier tape from the stratum corneum, removing the covering of fluid from the stratum corneum and drying the sheet of stratum corneum.

2. A method according to claim 1 further comprising removing the fluid from the underside of the screen by suction and recirculating the removed fluid to the upper side of the screen.

3. A method according to claim 1 further comprising feeding solvent fluid to said covering in a continuous stream extending around the whole periphery of said screen. 

1. A method of producing a substantially intact sheet of stratum corneum comprising the steps of applying a tape, bearing a pressure-sensitive, solvent-softenable adhesive, to a selected area of the skin of a human donor under conditions of heat and pressure, maintaining said tape on the skin of the donor for a prolonged period and removing said tape from said skin bearing an intact, unfissured layer of stratum corneum supported thereon, placing the carrier tape/stratum corneum composite unit on a fine screen in such manner that an uncovered area of the screen entirely surrounds the composite and the stratum corneum is in contact with said screen, supplying a solvent fluid, which exerts a softening action on the pressure-sensitive adhesive, in a continuous Stream to the upper surface of said screen to maintain a covering of fluid over the composite unit and replace fluid passing through said screen, while lifting one edge of the composite to just raise the edge of the underlying stratum corneum from the screen to initiate separation of the carrier tape from the stratum corneum sheet and thereafter carefully peeling the carrier tape from the stratum corneum, removing the covering of fluid from the stratum corneum and drying the sheet of stratum corneum.
 2. A method according to claim 1 further comprising removing the fluid from the underside of the screen by suction and recirculating the removed fluid to the upper side of the screen.
 3. A method according to claim 1 further comprising feeding solvent fluid to said covering in a continuous stream extending around the whole periphery of said screen. 